Schematic representation of the atomic force microscope interacting
with the material surface in research on investigating phase changes
in nanoscale materials. (Credit: Rama Vasudevan, ORNL)
(December 29, 2015) Understanding where and how phase transitions occur is critical to developing new generations of the materials used in high-performance batteries, sensors, energy-harvesting devices, medical diagnostic equipment and other applications. But until now there was no good way to study and simultaneously map these phenomena at the relevant length scales.
Now, researchers at the Georgia Institute of Technology and Oak Ridge National Laboratory (ORNL) have developed a new nondestructive technique for investigating these material changes by examining the acoustic response at the nanoscale. Information obtained from this technique – which uses electrically-conductive atomic force microscope (AFM) probes – could guide efforts to design materials with enhanced properties at small size scales.
The approach has been used in ferroelectric materials, but could also have applications in ferroelastics, solid protonic acids and materials known as relaxors. Sponsored by the National Science Foundation and the Department of Energy’s Office of Science, the research was reported December 15 in the journal Advanced Functional Materials.
“We have developed a new characterization technique that allows us to study changes in the crystalline structure and changes in materials behavior at substantially smaller length scales with a relatively simple approach,” said Nazanin Bassiri-Gharb, an associate professor in Georgia Tech’s Woodruff School of Mechanical Engineering. “Knowing where these phase transitions happen and at which length scales can help us design next-generation materials.”
In ferroelectric materials such as PZT (lead zirconate titanate), phase transitions can occur at the boundaries between one crystal type and another, under external stimuli. Properties such as the piezoelectric and dielectric effects can be amplified at the boundaries, which are caused by the multi-element “confused chemistry” of the materials. Determining when these transitions occur can be done in bulk materials using various techniques, and at the smallest scales using an electron microscope.